Negative environmental conditions (food shortage, pollution, …) may disrupt the development of an organism, and may therefore become apparent as deviations in specific morfological traits. This PhD research investigates the influence of environmental stress on the expression of different morphological traits in a butterfly, a cricket and a bird-species (resp. the Speckled wood Pararge aegeria, the House cricket Acheta domesticus and the Great tit Parus major). Based on the results of this study, we will critically assess the applicability of the use of deviations in morphological triats as bio-indicators of adverse environmental conditions.